Method and apparatus for producing vitreous enamel



Sept. 1, 1942. R. c; BOYD ETAL 2,294,328 I METHOD AND APPARATJS FORPRODUCING VITREOUS ENAMEL Filed Feb. 28, 1941 2 Sheets-Sheet 1 Sept. 1,1942. R. c. BOYD ETAL 2,294,828

METHOD AND APPARATUS FOR PRODUCING VITREOUS ENAMEL Filed Feb. 28, 1941 2Sheets-Sheet 2 V I Patented Sept. 1, 1942 METHOD AND APPARATUS FORPRODUQWG VITREOUS ENAMEL RobertC. Boyd, Harry C. Roach, and Charles E.McNeaL' Louisville, Ky.,.assignors to American Radiator & StandardSanitary Corporation, a corporation of Delaware Application February 28,1941, Serial No. 380,980

'3 Claims.

The present invention relates to the production of vitreous enameldirectly from molten enamel but without'the conventional quenchingoperations. The invention more particularly comprises procedure forproducing such enamel and equipment by means of which the new proceduremay be effectively carried out.

The important considerations which must be taken into account in thepreparation of vitreous enamel from molten enamel and the conventionalprocedures therefor have been outlined in application Serial No;254,424, filed February-3, 1939,

of which this application is in part a continuation. In thatapplication'it was pointed out that the ordinary quenching procedure,although extensively practiced, has recognized disadvantages which couldnot be avoided by existing practices. In that application it was alsopointed out that by following the procedure there set forth asconstituting the invention of that application many, if not all, of thedefects and disadvantages of prior practices could be eliminated and superior enamel produced at a very moderate cost. It has now beendiscovered that optimum results can be secured by following theadditional practices described and claimed in the present applicationand that matters of control along with other special features stillfurther improve the results.

It is, accordingly, one of the objects of the present invention to makeit possible to produce vitreous enamel in pure, uncontaminated form at arelatively high rate and at a comparatively low cost.

Another object of the invention resides in making it possible to producevitreous enamel by means of a novel procedure which involves simple butaccurate control of the material and the product during all stages ofproduction from molten to-finished state. i l

A further object of the invention resides in the provision of equipmentwhich makes it possibleto carry out the new procedure in a highlyeffective manner and without manual attention,

An additional object of the invention resides in relatively rapidlycooling a stream of molten enamel while shaping it into strip-like form,in

relatively slowly cooling such enamel in the form of a then plasticsheet to a temperature which is just above the annealing temperaturethereof, then in suddenly or rapidly lowering the temperature of theenamel below its annealing temperature to place it. in a highly strainedbrittle condition, whereupon it breaks up into self-drying-lglates andchips.

Other and further objects and advantages will be understood by thoseskilled in this art or willbe apparent or pointed out hereinafter.

In the accompanying drawings,

Figure 1 shows a front elevational view of parts of the equipmentconstituting the present invention andfragments of associated equipment;

Fig. 2 is an end elevational view looking from right to left at theparts of Fig. 1; and

Fig. 3 shows a fragmentary sectional view through the rolls duringoperation.

Like numerals designate corresponding parts throughout the views of thedrawings.

Describing the equipment with detailed reference to the drawings, itwill be observed that we employ a continuous melting furnace vIll of anysuitable or desired construction which per se forms no part of thepresent invention. This furnacerests upon the concrete or other flooringH which is suitably supported as by the metal beams and frameworkdesignated at H in any suitable or conventional manner, which likewise.per se form no part of this. invention. The furnace I0 is provided witha suitable discharge means such as the trough L3 which conveys moltenmetal from the melting chamber ll of the furnace to the orifice ortap-hole 15 in the refractory fore-hearth I6 on the front ofthe furnaceand which has a sight opening ll.

This furnace,-while of the continuous melting c type, may be, andpreferably is, such as to provide a substantialmolten body of enamel ofthe appropriate composition and character within the furnace so that acontinuous stream of molten enamel may be withdrawn from such moltenbody and discharged to the apparatus constituting our present inventionat a fairly constant temperature and viscosity. This preventsirregularities in production either with regard to continuity of theproduct or of variation thereof from a standard or mean which has beenemployed as the basis for the control factors hereinafter described andforming an important part of 7 this inventio s I The stream of moltenenamel descending from orifice I5 is received in the bight between the'rolls l8 and there forms a molten pool I9 hereinafter referred to. Theserolls are '50 mounted that they are capable of being rotated in oppositedirections at the same speed. These rolls are gear-driven from the gearmotor 20, the shaft 2| of which is provided with a gear 22 which,

' through a chain drive or the like 220, acts on gears or gearing 23 atone end of the rolls ll, thus driving said rolls at the desired rate ofpounds per hour.

speed. The bearings 2-4 of the rolls are mounted on the framework 25 sothat the roll shafts or journals l8a rotate therein, as will beunderstood by those familiar with rolls and their mountings. Means,marked 26, is provided of conventional nature for varying the spacingbetween rolls 3 and consequently varying the deforming fome exerted onmaterial between the rolls as well as controlling the rolledthickness ofsuch material.

The motor 20 is preferably of 7 H. P., 440 volt, three-phase and 60cycle. The motor shaft 2i has a speed of 13 R. P. M. The rolls l8 are12% inches in their outside diameter and are water-cooled, as is bestnoted at 21 in Fig. 3. The rolls are revolved by the motor at R. P. M.,and thus the calculated surface speed thereof is equivalent toapproximately 32.3 feet per minute. The cooling water 21 is pumped tothe interior of the rolls at the rate of approximately 60 gallons perminute and under average operating conditions there is approximately a 6F. rise in temperature in the cooling water.

The stream of molten enamel issuing from the furnace and entering thebight between the rolls is rapidly cooled and deformed by said rolls.Whereas the temperature of the molten enamel as it enters the bight isin the neighborhood of 1800 F. (:50), it will, of course, be

gone before, the precise temperature of the plastic sheet will varysomewhat depending somewhat upon the enamel composition. -We have foundthat the temperature of the plastic sheet should range betweenapproximately 1000" F. and 1400 F. for effective consistent results.

It will be appreciated, however, that the width and thickness of thesheet may beyaried or controlled and that wide sheets as well as narrowones can be equally well produced. The equipment must furthermore be.correlated with the particular melting furnace which must be ofadequate capacity to supply sufllcient molten enamel for the purposes ofour present invention.

The plastic sheet-like enamel now is in the form of a descending ribbonI9a, the speed of which is governed by the surface speed of the rollsl8. Therefore, under the conditions above recited it can be calculatedthat the descending enamel has an acquired speed of approximately 32.3feet per minute. This descending ribbon of enamel givesup its heat inaccordance with its temperature gradient with respect to the surroundingtemperature and its speed of movement but this rate is relatively slowas compared to the abrupt reduction in temperature due to passagethrough the rolls and also with relation understood that the precisetemperature is de- I pendent upon the composition of the particularenamel being handled. The temperature must be high enough so that theenamel is in the form of a readily flowable mobile liquid. For the variious compositions ordinarily encountered the tem-' perature of the moltenenamel may range from about 1700 F. to about 2000" F. The temperature ofany particular composition should be fairly closely controlled to withinapproximately In its passage between the rolls l8 the stream perature byseveral hundred degrees and at the same time is converted intosheet-like plastic form. The rolls are preferably so set or adjusted asto produce a sheet which is of the order of ,6 in thickness. In theconversion of the molten stream to the plastic sheet-like form it will,of course, be understood that aconsiderable width is imparted to thesheet. This width depends upon certain factors which will be understoodor hereinafter referred to but we have found that a sheet approximately18" in width is equivalent to a smelting rate of about .1000

The rate of rotation of the rolls, the spacing therebetween and the rateof discharge and temperature of the stream of molten enamel are all socorrelated that a substantial pool of molten enamel, heretoforedesignated. as I9, is formed and maintained in the. bight between saidrolls. This molten pool should be maintained of such size that itsapproximate depth at its center is not less than about 3" to 4". A poolof this volume and character not only has definite influences upon thesubsequent operations and the of enamel is rapidly and suddenly loweredin temto the subsequent reduction in temperature hereinafter described.To protect the descending ribbon of enamel and to prevent contaminationthereof, it preferably passes through a tapering stainless steel hopper28, the larger end of which is directed upwardly to receive the enamelfrom the rolls; This hopper 28 is provided with a suitable inspectiondoor 29 which may be opened for test or examination or may be providedwith a transparent sight glass section (not illustrated) in order thatthe production may be observed at all times so as to check upon theappearance, continuity and dimensions of the product.

The vertical height of this hopper may be varied in accordance with theenamel composition or the circumstances of the installation. In itspassage through this hopper the enamel relatively slowly becomes reducedin temperature until it approximates a temperature which is just abovethe annealing temperature of that particular composition. In the presentinstance this temperature is approximately 950 F. (1 50) but thetemperature at this point should be within the range of approximately800 F. to

1100 R, which range of temperature covers than thesucceeding andpreceding temperature reductions. Within the purview of this invention,however, we may introduce air or other fluid cooling medium (liquid,gaseous or both) into the hopper at such temperature and rate as toeffect the proper amount of cooling. In other words, we may control thetemperature and/or atmosphere of said hopper and its interior. v

As the descending ribbon of enamel leaves the bottom or smaller end ofsaid hopper 28,-lt is received by the vibrating pan conveyor 29. This ismounted at a slight angle of inclination, as will be noted from Fig. l,and the en amel is received in the lower part thereof. As the enamelpasses into such conveyor it breaks up into large flat plates 30 whichroughly vary from about 4" to 12" in extent or diameter.

The vibratory action is oi such nature as to cause these enamel platesto ascend in the pan conveyor at until they reach the upper end thereof,at which point they drop of! the conveyor into the second vibrating panconveyor II which, while also slightly inclined from the horizontal, ismounted substantially at right angles to the first vibrating panconveyor 29. 7

As the plates 30 reach the upper end of con-' veyor 29 and as they dropinto the lower end of conveyor 3|, they are subjected to vigorouswetting and cooling action by one or more water sprays 32. These watersprays are discharged with the requisite force and direction by meansoithe spray nozzles 33 which receive cold water from a suitable supplyor source and which discharge that water as sprays in the approximateproportion of 1 gallon of water to each 250 pounds of enamel. While asingle spray has been shown for convenience and simplicity in connectionwith each conveyor, it will, of course, be understood that additionalnozzles may be employed for producing the required cooling eflect overthe required area.

Under the conditions just set forth the enamel undergoes a relativelyrapid reduction in temperature until that temperature is reduced belowthe annealing temperature or temperature range for the particularcomposition involved. For an enamel composition responding to theparticular temperatures hereinabove specified. the temperature reductionby means of the spray nozzles should reduce the temperature. to lessthan 750 F. but not below approximately 300 F. In this manner the abruptor drastic cooling causes the enamel chips at which result to be in ahighly strained and .brittle condition and composition.

to retain sufilcient internal heat to render the chips self-drying, thuseliminating the usual drying operation in connection with prior artprocedures. The enamel chips which spontaneously form in the conveyor 3|are ordinarily from to 3" in extent or diameter and aresuitable fordirect feed into a grinding mill which reduces them to the desired stateof subdivision, preferably to a fine powdered form.

-It will be understood that suitable equipment is provided for vibratingthe conveyors 29 and hi but in the drawings we have only illustratediragmentarily conventional equipment 36 for vibrating the conveyor 29.The precise details of such are immaterial and form no restriction uponour present invention.

In describing the apparatus which constitutes a part of our presentinvention we have at the sametime set forth the procedures which arewith the discharge of a continuous stream of.

molten enamel from a suitable furnace and concludes with the spontaneousformation of the chips 8G in conveyor ii. The stream of molten tion theenamel is'converted'to sheet-like form.

This plastic sheet is discharged 'continuouslyi from the rolls anddescends a certain vertical distance while being further cooled but at arelatively slower rate to atemperature which is just above the annealingtemperature of that against a vibrating pan conveyor wherein it breaksup into plate-like form and from that conveyor it passes to a secondvibrating conveyor where it spontaneously takes a chip-like form. Duringthe transition the temperature is rapidly or abruptly lowered throughthe annealing range so as to place the enamel in a highly strainedbrittle condition.- By annealing tem-- perature or annealingrange asherein employed, we mean that temperature or range'of temperatures at orwithin which an enamel, glaze or vitreous composition is ordinarily heattreated to relieve strains and to put it in a tough, strong form inwhich it is not readily shatterable and in which it is substantiallyfree of internal stresses.

The present invention comprises both appazratus and procedure, andwithin the spirit and scope of the appended claims .we may make variousadditions, omissions, substitutions and modifications, and in any eventthe foregoing description is to be understood as being illustrative orexemplary and not as limitative or restrictive. Depending upon theparticular composition and its critical temperatures, we 'may, make suchchanges in the size, speed and nature of the equipment as will bedesigned to take care of material of the particular kind involved. I

Having thus described our invention, what we claim as new and desire tosecure by Letters ,Patcut is:

1. A method of producing enamel chips directly from molten enamel whichcomprises discharging a stream ofmolten enamel which has been raised toa temperature or about 1700-2000 F., intercepting such stream andsubstantially simultaneously cooling and deforming it to lower itstemperature abruptly and to convert it toplastic sheet-like form at atemperature of about loco-moo E, further cooling the sheet-like enamelat a relatively slow rate until it reaches a temperature of about800-1100 F2, which is.

just above the annealing range of the particular composition involvedand then rapidly cooling the enamel to a temperature below its annealing1 range and below about 750 F. but not less than tively slow rate untilit reaches a' temperature enamel is acted upon by a pair of rolls whichrapidly reduces the temperature thereoi under the conditions noted to atemperature at which the material is in a plastic condition, i. e.,- isI 'intc powder form.

about 309 F., whereby the enamel spontaneously breaks up first intoplates and then into chips which are brittle and highly strained andwhich are in a condition favorable for 2. A method or producing enamelchips. directly from molten enamel which comprises dischargin a streamof molten enamel, intercepting such stream and substantiallysimultaneously cooling and deforming it to lower im temperature abruptlyand to convert it to plastic sheet-like form, further cooling thesheet-like enamel at a relaiust above the annealing range of theparticular 1 tion involved and then rapidly cooling the enamel to atemperature below its annealing range by spraying it with a coolingfluid, where-v by the 2;. I I plates and then into chipa which arebrittle and hmhly strained and which are in a ccndiuon iavorablc to: newconversion to powder form The descending enamel impinges" readyconversion V-.-..= spontaneously bmss up first into 1 and subjecting theenamel to the influence of vibration during the chip-forming stage.

3. Apparatus for producing enamel chips directly from molten enamelwhich comprises a pairof water-cooled rolls capable of being slowlyrevolved in opposite directions at the same speed, a taperinghopper-like receptacle below said rolls and the upper larger end 01'which is disposed to receive enamel discharged in plastic sheet -likeform from said rolls, an inclined vibrating conveyer underneath thelower smaller end of the hopper-like receptacle and disposed to receiveenamel therefrom, said conveyer being inclined upwardly from thereceptacle, a second and similar conveyer angularly disposed withrespect to the first conveyer and arranged to receive enamel in itslower portion from the first conveyer and means for introducing acooling fluid into said conveyers.

4. Apparatus as set forth in claim 3 in combination with means fordischarging a stream of molten enamel to the bight between said rollsand means for correlating the rateot discharge thereof with the rate ofrotation of the rolls to form and maintain a substantial molten pool orenamel in the roll bight having a depth at the center thereof of about3-4 inches.

5. A method of making vitreous enamel which comprises the steps ofdischarging a stream of molten enamel, at a temperature above themelting range thereof, into the bight between two cooling and formingrolls rotating at the same speed in opposite directions, withdrawingenamel from said bight, controlling such withdrawal so as to form andmaintain in said bight a substantial molten pool of said'vitreousenamel, said enamel being withdrawn in a plastic sheet-like form at atemperature in the neighborhood or 1300 1"..iurther lowering thetemperature thereof to about 1100 R, which is just above theannealingvrange o! the particular enamel composition by bringing it intocontact with a cooling medium and finally converting the enamel to abrittle strained condition by further reduction in temperature throughthe annealing range to about 750 FL, by bringing it into contact withanother cooling medium whereupon it spontaneously breaks into fragments.

6. A-method or making vitreous enamel which comprises the steps ofdischarging a stream or 5 molten enamel into the bight between twocooling and forming rolls rotating at the same speed in oppositedirections, withdrawing enamel from said bight, controlling suchwithdrawal so 'as to form and maintain in said bight a substantialmolten pool oi said vitreous enamel, said enamel being withdrawn in aplastic sheet-like form at v a temperature in the neighborhood of 1300F. due to rapid lowering oi temperature by contact with said rolls,bringing the plastic sheet-like v enamel into contact with a coolingmedium which relatively slowly lowers its temperature to about 1100 F.which is just above the annealing range of the particular enamelcomposition and then converting the enamel to a brittle strainedcondition by quickly shock cooling it through the annealing range toabout 750 F. by contact with another cooling medium, whereupon itspontaneously breaks up into fragments.

7. A method of making vitreous enamel which comprises the steps ofdischarging a stream 01' molten enamel into the bight between twocooling and forming rolls rotating at the same speed in oppositedirections, withdrawing enamel from said bight in a descending, plasticsubstantially continuous sheet-like form at a temperature in theneighborhood of l300 F., so correlating said discharging and withdrawingsteps as to form and maintain a substantial pool of molten enamel inthesaid bight, contacting the descending sheetlike enamel with a coolingmedium which reduces F. at a relatively initial cooling between rollsand then shock-cooling the enamel through its annealing range bybringing it into contact with another cooling medium which lowers itstemperature rapidly enough to convert the enamel to a strained brittlecondition, whereupon it spontaneously breaks up into sell-drying tragitstemperature to about ll00 slow rate compared with the ments. c ROBERT C.BOYD.

HARRY C. ROACH.

cmanns E. McNEAL.

